Selena Gomez almost got caught with her pants down!

The sexy songstress must have done the ol' unbutton the jeans and unzip the first inch or two so you can relax and breathe during an international flight ... but her plan backfired because as soon as she sees these pix, she's not going to be so relaxed!

After a whirlwind vacation with Justin Bieber in the Caribbean and then a few days in the City of Lights for Paris Fashion Week, Gomez reluctantly returned to the U.S., on Wednesday, while bad boy Bieber stayed behind ... to cause trouble, no doubt.

The Biebs already lunched with Kendall Jenner -- without Selena -- the other day in Paris. Last night he was out on the town with Paris Hilton. What's next? Dinner with Miranda Kerr?